Current global demand for the carbon emission reduction and the depletion progress of high-grade iron ore deposits require the integrated solution toward sinter and ironmaking process. Several countermeasures have been proposed regarding the development of highly reducible burden materials for the blast furnace and the use of beneficiated fine iron ores in the sintering machine. However, their application to actual sintering and ironmaking equipment have been limited because the sinter productivity is deteriorated. Here the present study investigated co-production of the carbon composite pellet and sinter with existing sintering machines. Even if fired in an oxidizing atmosphere, carbon-core-pellets can be produced under conditions that simulate the conventional sintering process. This is because a protective shell over the carbon core inhibits the carbon from combustion. Importantly, the structure and composition of the pellets are properly designed so that this protective shell does not melt overly or break during firing. The design parameters govern the strength and reducibility of pellets after firing, and those influence is analyzed quantitatively. Overall, a pot test trial in which designed pellets have been blended exhibited the viability of the pellet-sinter co-production.

The pellet making method was studied for production of iron ore pellets with a carbon core. The pellets are to be fired in a sintering machine to produce sintered ores containing carbonaceous material. This new raw material for the blast furnace will have advantages such as high reducibility and low slag generation. In this study, pellet making tests were performed using laboratory and pilot scale disc pelletizers with 3 to 5 mm coke breeze, concentrated iron ores and additives in order to construct a method for producing pellets with a carbon core. Scaling-up of the method was considered with four discs with diameters of 0.6, 1.2, 2.0 and 3.5 m. As a result, it was found that there were two strategies for producing pellets with a carbon core at high yield: supplying a suitable level of water with a small droplet size, and spraying water in a specific area where the coke breeze flows on the surface of the contents in the disc. This study demonstrated that iron ore pellets with a carbon core can be obtained at a yield of more than 90% by using the disc pelletizer with the 3.5 m diameter. It was also estimated that a production capacity of 70 t/h can be expected with a 7.5 m diameter disc for commercial scale operation. This achievement of constructing a method for producing pellets with a carbon core was a breakthrough which overcame one of the technical hurdles for the development of sintered ores containing carbonaceous material. KEY WORDS: iron ore pellet; carbon core; pelletizing; high reducibility; low slag.

With the aim of developing an iron ore sinter with a better reducibility, the authors researched the co-firing of green pellets and a sinter mix in a packed bed. First, a physical simulation with a simulator for the charging equipment of a sintering machine demonstrated that the green pellets were distributed more strongly to the lowest part of the packed bed because their size is larger than that of the sinter mix. Pot tests based on the simulated pellet distribution proved that it is possible to produce a highly reducible sinter at higher productivity, particularly when a concentrate with a large Blaine surface area is used to produce rigid green pellets. Factors that could reduce product yield were also pointed out, i.e., diffusion of the melt from the sinter mix into the pellets and a larger local heat supply to the sinter mix than is suitable. These factors are thought to hinder the formation of thick and strong bonds in the co-fired sinter bed. A 450 kV class X-ray CT was used to visualize the internal structure of the sinter plugs, and revealed the plug made with the green pellets has higher porosity, which is important for better permeability, but also results in less bond formation, which reduces the yield in a co-fired plug. These findings revealed insights for fully enjoying the advantages of co-firing green pellets and sinter mix, as well as issues to be overcome in order to realize a successful co-firing process.